The alkylation of aromatic compounds with olefins to produce monoalkyl aromatic compounds is a well-developed process that is practiced commercially in large industrial units. One commercial application of this process is the alkylation of benzene with ethylene to produce ethylbenzene, which may subsequently be used to produce styrene. Another application is the alkylation of benzene with propylene to form cumene (isopropylbenzene), which may subsequently be used in the production of phenol and acetone. Those skilled in the art are therefore familiar with the general design and operation of such alkylation processes.
Alkylation processes generally involve alkylation of aromatic compounds with olefins in the presence of alkylation catalyst. In particular, it is known to conduct alkylation processes in a multi-bed alkylation reactor that includes at least two separate alkylation stages, with the alkylation stages each including an alkylation catalyst bed. Such multi-bed alkylation reactors can be effectively utilized to maximize yield of alkylation products. To maximize a useful life of conventional alkylation catalysts, techniques have been developed for maintaining reaction temperatures in the separate alkylation stages within a particular temperature range, with little difference in reaction temperature between the various alkylation stages. Under uncontrolled conditions, reaction temperatures tend to be highest in the first alkylation stage due higher reaction rates prevalent therein. Because less available unreacted aromatic compounds are generally present in downstream alkylation stages, reaction rates and, thus, reaction temperatures tend to be lower in downstream alkylation stages.
To enable greater temperature control in the various alkylation stages, one development that has been made is to recycle unreacted aromatic compounds from product effluent to both the first alkylation stage and to downstream alkylation stages in the alkylation reactor. For example, it is known to distill unreacted aromatic compounds from the product effluent, followed by recycling the unreacted aromatic compounds to the various alkylation stages in the alkylation reactor. In this manner, reaction rates and reaction temperatures can be controlled in the various alkylation stages. It is also known to recycle some of the reactor effluent to the various alkylation stages, without distilling the unreacted aromatic compounds, also for purposes of controlling temperatures in the various alkylation stages of the multi-bed alkylation reactors.
Despite the developments involving recycling reactor effluent and/or unreacted aromatic compounds that have been proposed to date, selectivity of monoalkyl aromatic compound formation is impacted by such developments. In particular, recycling of the reactor effluent can result in a higher incidence of dialkyl- and/or trialkyl-aromatic compound formation. The reactor effluent generally includes large quantities of monoalkyl aromatic compounds, and returning such monoalkyl compounds to the various alkylation stages risks further reaction of the monoalkyl aromatic compounds to produce the dialkyl- and/or trialkyl-aromatic compounds, thereby decreasing selectivity of monoalkyl aromatic compound formation. Further, techniques that involve distilling the unreacted aromatic compounds from the product effluent, followed by recycling the unreacted aromatic compounds to the various alkylation stages in the alkylation reactor, as described above, require significant energy expenditures to vaporize and condense the unreacted aromatic compounds. While selectivity of monoalkyl aromatic compound formation can be increased by increasing a ratio of aromatic compound to olefin, lower ratios of aromatic compound to olefin are desirable from an energy cost standpoint.
Accordingly, it is desirable to provide processes for preparing alkylated aromatic compounds that enable maximized selectivity of monoalkyl aromatic compounds to be achieved while recycling reactor effluent that includes the desirable monoalkyl aromatic compounds present therein. It is also desirable to provide such processes that enable maximized selectivity of monoalkyl aromatic compounds to be achieved without increasing a ratio of aromatic compound to olefin. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.